A powered vehicle, such as an aircraft, car, or boat, often includes one or more batteries for starting the vehicle's engine and/or providing electrical power to the vehicle's systems. For example, vehicle power systems sometimes include lithium-ion, lead-acid, or nickel-cadmium batteries. Such batteries generally include a negative terminal and a positive terminal immersed in an electrolyte solution. Vehicle batteries may include multiple battery cells connected in series with a negative and positive terminal for providing power to the vehicle and vehicle engine. The battery cells and pair of terminals connect to the electrical system of the vehicle.
Some batteries must incorporate electronic protection to prevent the battery cells from being damaged or becoming unstable from abusive conditions and/or accidental discharge, such as excessive charging voltage or current, excessive discharge current, or excessive depth of discharge. When incorporating these electronic protections into a battery for vehicles, the battery needs to allow for sufficiently high discharge of current to complete the engine start profile. Additionally, the battery needs to be disconnected if subjected to: (i) a current load exceeds the engine start profile (e.g., a low resistance external short circuit); or (ii) to an excessive depth of discharge. Irreversible damage to a battery may be caused by current loads exceeding the engine start profile or excessive depth of discharge.
One approach to solving this challenge for batteries is to incorporate a normally opened contactor in the power circuit between the battery cells and the terminals of the battery. An external switch, which is in an open or closed position, may be mounted on the exterior of the battery or wired in the vehicle. The external switch may energize the coil of the contactor and bring contacts into a closed position. When the external switch is open, the battery is protected from excessive current or excessive depth of discharge. When the external switch is in the closed position, the contactor circuit closes, and the battery is ready to perform the engine start profile. The disadvantage of this approach is the necessity of installing and operating the external switch, and thus adding complexity to the vehicle design and operation.
Another approach to solving this challenge is for batteries is to incorporate a normally closed contactor in the power circuit between the battery cells and the terminals of the battery. With this approach, an external switch is not required to perform an engine start profile. However, power is required to energize the coil and keep the contactor open. If the contactor is opened to protect the battery from excessive current or excessive depth of discharge, the coil requires ongoing power consumption that may completely drain the battery cells of energy and damage the battery.
Excessive current, which may be also be referred to as overcurrent, is a situation where a larger than intended electric current exists through a conductor. This may lead to excessive generation of heat and increased potential for fire hazards. The depth of discharge is the portion of the nominal capacity from a cell or battery removed during each discharge cycle, which is expressed as a percentage. Shallow depth of discharge may be 10% or less level of discharge, where deep depth of discharge may be 80% or more level of discharge.